1) Field of the Invention
The present invention relates generally to agricultural implements and, more specifically, to flexible frame structure for large folding implements such as air drills.
2) Related Art
Large folding implements including a tillage type frame have sections hinged together for folding about fore-and-aft axis for movement between a folded or raised transport position and unfolded field-working position. One problem with many such implements is lack of flexibility of the frame which results in uneven working depth of the tools in non-level ground conditions. If the implement is used for seeding, the planting depth can vary unacceptably, and the openers can actually lift out of the ground in some conditions. To alleviate problems caused by relatively inflexible frames, some large implements, such as the Flexi-Coil model 5000 air hoe drill, provide frames with opener-carrying tubes supported by resilient joints. One type of flexible joint arrangement is shown in U.S. Pat. No. 4,977,964 which is assigned to Flexi-Coil Limited. Although such a frame structure provides flexibility to follow irregular ground contours, the resilient joints allow the frame tubes and openers mounted thereon to rotate about an axis perpendicular to the direction of travel. Such rotations results in inconsistent opener depth control. The resilient joints require specially manufactured components that are subject to wear. Providing frame section flexibility without excessive section distortion and rotation of the frame tubes has been a continuing problem.
Another type of large frame for tillage implements, such as shown in U.S. Pat. No. 4,102,404 issued to Kelly A. Krammer, has a frame section that utilizes a generally L-shaped frame member having an aft transverse member connected to an adjacent frame section by a universal joint and a front transverse member connected by a universal joint to the end of the L-shaped member. Only two ranks are available for mounting tools on such a frame section, and a large front brace member is necessary to provide fore-and-aft stability for the section. The frame also requires ground wheels supported under portions of the front and aft transverse members, and the wheels limit flexibility in the available spacing arrangements of the openers or other tools on the transverse members. Further types of flexible frame structures include special hinge joints between sections or angled axis arrangements, and many require relatively massive forward hitch or brace structure extending between all the sections.